The invention relates to a method and to an application apparatus for applying a transfer ply of a foil to a substrate, and also to a printing apparatus featuring an application apparatus of this kind.
The coating of foils or substrates by digital printing techniques for foil application serves to generate additional decorative effects. It typically involves the application of a cationically curing adhesive directly to the substrate or the foil by means of inkjet printing. The adhesive is solidified by means of a drier unit operating cationically. Mediated by the adhesive, the layers of the foil to be applied adhere to the substrate and are subsequently detached from a carrier ply of the foil. A known alternative to this is to use xerographic printing techniques to apply a thermoplastic toner to the substrate. On application by means of pressure and heat, and mediated by the toner which melts as a result, the layers of the foil to be applied adhere to the substrate and are subsequently detached from a carrier ply of the foil.
On inkjet printing of the adhesive directly onto the substrate, with subsequent foil application, an acceptable quality cannot be produced, owing to the adhesive running and being drawn under suction into the substrate. Foil application under pressure with a press roll exacerbates this situation. Because of the pressure and the running of the adhesive, fissured foil edges are produced on the substrate. The foil topping, moreover, often has holes in it. The gloss of the foil surface following application to the substrate is heavily dependent on the nature of the substrate surface. On nonabsorbent substrates, examples being plastics such as PE, PP or PET, the adhesive is quickly displaced widthwise by the press roll. Overall, therefore, it is usually not possible to ensure high-resolution foil application with precise edges.